Display devices produced by using liquid crystalline compounds (the term "liquid crystalline compounds" is used in this specification as a general term for the compounds which exhibit a liquid crystal phase and for the compounds which do not exhibit a liquid crystal phase but are useful as component of liquid crystal compositions) have widely been utilized for the display of watches, tabletop calculators, word processors, or the likes. In recent years, researches on in-plane switching (IPS) mode and vertical alignment (VA) mode by which viewing angle can be improved at a moderate cost have extensively been conducted.
For the liquid crystal compositions used in these modes, such physical properties as a high voltage holding ratio, low threshold voltage, small their dependency on temperature, low optical anisotropy value (.DELTA.n), wide temperature range of liquid crystal phase, excellent miscibility with other liquid crystal materials, and low viscosity have been sought.
As the component of liquid crystal compositions having such characteristics, many liquid crystalline compounds in which fluorine atom substituted at a lateral position were investigated, and patents disclosing, for example, the following compounds are published:
##STR1## 1) (Laid-open Japanese Patent Publication No. Hei 2-233626) ##STR2## 2) (Tokuhyo (Laid-open Japanese WO publication) No. Hei 2-503441) ##STR3## 3) (Tokuhyo (Laid-open Japanese WO publication) No. Hei 6-504032) ##STR4## 4) (DE 3,839,213 A1)
Whereas the compounds of the formula 1) or 2) have a low .DELTA.n, their threshold voltage is high. Whereas the compounds of the formula 3) or 4) have a low threshold voltage, their .DELTA.n is high. Thus, these compounds can not be said to have satisfied the requirements mentioned above.
Chlorine substituted compounds are disclosed, for example in 5) DE 2,933,563 and 6) DE 4,219,819.
A part of the compounds expressed by the general formula (1) are formally included in the prior literature 5) or 6) mentioned above. However, as to the compounds of the present invention, data such as physical properties are not described at all and their characteristics are not specifically mentioned in the prior publications. Thus, the publications have not suggested the utility of the compounds of the present invention.